1. Field of the Invention
The present invention relates to a method for the production of lean meat-containing animals. Specifically, the invention relates to a method for the regulation of protein and fat content in animals by hyperimmunization.
2. Brief Description of the Background Art
The production of food animals containing a relatively high protein content and a relatively low fat content is a major goal of food providers. See Sun, M., Science 240: 136 (1988); and "Designing Foods: Animal Product Options in the Marketplace," Committee on Technological Options to Improve the Nutritional Attributes of Animal Products, Board on Agriculture, National Research Council, National Academy Press, Washington, D.C., 1988.
Animal food products are a major source of fat calories in the consumer diet, supplying about 36% of the caloric intake. Animal food products account for 57% of the fat consumed in the typical American diet and have been implicated as an important factor contributing to the development of heart disease and other related ailments. The American Cancer Society (1984), American Heart Association (1986), National Institutes of Health (1984) and the National Research Council (1982) have all recommended that 30% or less of the total caloric intake of adults be in the form of fat. Designing Foods supra, p. 15. Although consumer eating habits are changing and less red meat is being consumed, a recent report from the National Academy of Sciences, which evaluated ways to reduce the contribution of animal food products to the dietary fat intake, concluded that "the real solution lies in the production of leaner animals" Designing Foods, supra, p 3.
Current methods of producing lean animals and meat utilize hormones to increase the body protein to fat ratio, "Designing Foods", supra, and Mersmann, H. J., Prog. Food Nutr. Sci. 11:175-201 (1987). Hormones that have been used to regulate the carcass ratio of protein to fat include anabolic steroids, growth hormone, and adrenergic agonists.
Anabolic steroids have been effectively administered to ruminant species and especially to beef cattle for the purpose of manipulating carcass protein content. A ruminant animal being fed anabolic steroids produces more muscle and less fat. However, anabolic steroid treatments are not effective in non-ruminant species. In addition, consumer concern over possible residual levels of anabolic steroids in the food product itself have led to pending legislation in many countries proposing a complete ban of this method. The European Community banned the use of steroids in 1988.
Changes in body composition induced by growth hormone are similar to those induced by anabolic steroids; that is, growth hormone induces the accumulation of more muscle and less fat. In addition, growth hormone is effective in both ruminant and nonruminant species. Research efforts in this area have recently been focused on the creation of genetically modified animals containing a regulatable growth hormone gene such as zinc-regulatable human growth hormone. Sun, M., Science 240:136 (1988), and Miller, C., Gen. Eng. News, May 1987, p. 7. In theory, the zinc-regulatable human growth hormone gene would be induced or repressed at appropriate periods in the animal's growth by altering the levels of zinc in the diet. However, this approach has not been completely successful. In pigs the gene appears to be "leaky," that is, continuously expressing whether or not the diet is supplemented with zinc, Marx, J. L. Science 242:32-33 (1988). Because of the overproduction of growth hormone, the transgenic growth hormone pigs have some serious abnormalities; females are sterile, and both males and females are generally susceptible to arthritis and gastric ulcers which often are fatal. Marx, J. L., Science 242:32-33 (1988). In addition, as with steroid treatment, consumer acceptance of meat from growth hormone genetically engineered cattle has been a major problem. Sun, M., Science 240:136 (1988).
Analogs of the .beta.-adrenergic agonists epinephrine and norepinephrine, especially clenbuterol and cimaterol, have been used to increase carcass protein levels in food animals. Muir, L. A., Designing Foods, supra, pp. 184-193. These agonists, while they have only small effects on weight gain and feed efficiency in the animals, tend to stimulate lipolysis and thus change the total body composition to a higher protein, less fat composition. However, chronic feeding may cause hypertrophy of skeletal muscle and some food species, such as chicken, are poor responders. Also, .beta.-agonists are usually included in the diet and therefore are not suitable for use with grazing animals. Lastly, as with the other hormone treatments, there is a strong public opposition directed against eating meat from .beta.-agonist-treated animals.
Normally, upon exposure to a foreign antigen, e.g., a bacterium, the immune system of the host will produce antibodies that will neutralize the effects of the antigen. Exposure to such foreign antigens can occur either naturally, or deliberately by administration of the antigen in vaccine form. The latter is generally referred to as active immunization of the host species exposed to the antigen. The antibodies produced in response to such vaccination are homologous to said given species of animal, and are epitopic to the antigen. In general, merely inducing an immune state in an animal does not alter the levels of carcass fat or protein, Williamson, E. D., et al., Livestock Prod. Sc. 12:251-264 (1985).
To avoid the problems associated with exogenous hormone administration, attempts have been made to regulate animal growth immunologically, by actively immunizing the animal against a specific component or hormone, the lack of which promotes the development of a relatively lean animal. For example, a single injection, into growing rats, of antibodies raised against fat cell plasma membranes, significantly lowered the levels of body fat and the number of fat cells in the rats for a period of several months. Flint, D. J., et al. Hannah Res. (1985), pp. 123-127. However, immunizing against fat cells per se makes it difficult to control the level of body fat on an animal. Animals that are overly lean would suffer from some of the same serious problems that the transgenic growth hormone-containing pigs do due to their overly lean growth, for example, sterility. In addition, meat from overly lean animals has a tendency to be tough, and lacks succulence and flavor. Speer, V. C., in Designing Foods supra, pp. 273-277. A minimum of 3% fat (uncooked) has been recommended as the minimum percentage required for palatability of broiling cuts of meat. Savell, J. W. et al., Designing Foods, supra, pp.345-355.
Attempts have also been made to increase growth hormone levels in growing animals by immunizing lambs and beef cattle against somatostatin, the hormone responsible for suppression of growth hormone. This method has also been tried on sheep and has been recently reviewed. Designing Foods, supra, Chapter 6, pp. 115-132; and Schelling, G. T. et al., Designing Foods, supra, pp. 200-207. In theory, by immunizing against somatostatin, the levels of somatostatin would decrease and thus the levels of growth hormone increase. However, this method has produced conflicting results. Spencer, G. S. G., et al., Livestock Prod. Sc. 10: 25-37 (1983). Lambs immunized repeatedly against somatostatin grew larger, faster, and were heavier than non-immunized lambs but there was no change in the proportion of muscle or fat. One study, which compared the carcass composition of lambs repeatedly immunized against somatostatin using lambs of equal weight (rather than equal age), suggested that at any given weight, the carcass of the immunized lamb was leaner. Spencer, G. et al., Anim. Prod 40:523 (1985). However, repeatedly immunizing with a purified hormone such as somatostatin is relatively expensive when treating large numbers of herd animals.
It has been known in the prior art to produce a hyperimmune state in an animal wherein that hyperimmune state produced a milk having a variety of therapeutic effects. Beck, for example, has disclosed a milk containing antibody to Staphylococcus mutans that has dental caries-inhibiting effects (Beck, U.S. Pat. No. 4,324,784; British Patent 1,505,513). Beck has also described a milk having anti-arthritic properties, U.S. Pat. No. 4,732,757, and has patented a method of treating inflammation using milk from hyperimmunized cows, Beck, U.S. Pat. No. 4,284,623. Stolle et al. have disclosed a method of using milk from a hyperimmunized cow for the treatment of diseases of the vascular and pulmonary systems, U.S. Pat. No. 4,636,384.
In addition, in U.S. Pat. No. 4,636,384, there was disclosed a method of lowering blood lipid levels and treating lipid-associated vascular disorders, as well as treating macrophage-related pulmonary disorders, comprising feeding test animals and humans milk derived from cows maintained in a hyperimmune state.
Other authors have noted the ability to derive therapeutic products from the milk of mammals by specifically immunizing or hyperimmunizing those animals against a known antigen. Heinbach, U.S. Pat. No. 3,128,230, Singh (U.S. Pat. No. 3,911,108), Peterson (U.S. Pat. No. 3,376,198 and Canadian Patent 587,849), Holm (U.S. application (published) Ser. No. 628,987), and Tannah et al. (British Patent 1,211,876), and Biokema S. A. (British Patent 1,442,283).
However, no suggestion or speculation is made in any of these references that the hyperimmune state itself alters the metabolism of the animal so as to increase the ratio of body carcass protein to fat. Placing an animal in a hyperimmune state has been reported to increase the concentration of proteins in the serum, Srinivasan, V. A., et al., Indian Veterinary Journal 54:1-5 (1977); and Janos, S. et al., Magy Allatory Lap 20:487-490 (1965). However, changes in serum protein levels do not necessarily correlate with levels of carcass protein and fat content, and neither report noted any effect of hyperimmunization on the carcass protein or fat content of the animal.
Thus there remains a need for methodology for the production of lean food animals. Such would be methodology that does not physiologically impair the animal. Such methodology would result in a food product acceptable to the consumer, yet be technically simple, and economically applicable to large numbers of herd animals and especially to grazing animals.